New USES=twisted, to replace the old USE_TWISTED knob.
twisted can be configured with the arguments run or build to replace
the previous USE_TWISTED_RUN and USE_TWISTED_BUILD knobs. The twisted
components can be added as comma-separated arguments. If you previously
wrote
USE_TWISTED= yes
USE_TWISTED= conch names
USE_TWISTED_RUN= yes
you now would write
USES= twisted
USES= twisted:conch,names
USES= twisted:run